What on earth does the Trinity have to do with me? God is three in one? How is that supposed to work? These are not stupid questions. The Trinity is the first article of religion and by far the most difficult to understand. In fact, you cannot understand it. I can’t understand it. Not in the way we understand every other object or form of knowledge in creation. You may not understand exactly how a computer works, but someone does. And, if need be, you can find the expert and given enough time and interest, you can learn how computers work to the point that you would understand.
God is not an object like other objects. God is not a creature like other creatures. God is not this really powerful being really far away telling us what to do, controlling us like puppets. God is the source of all existence, all being. As Paul says in Acts 17, God is the one in whom we live, move, and have our being.
We believe that God is triune, Father, Son, and Holy Spirit, three persons, of one substance, because it has been revealed to us. It is an act of faith. Here are three analogies that I find helpful when approaching the Trinity. Each has its virtues but each is also limited.
Fire: It is written, “Our God is a consuming fire” (Heb 12:29) Fire can be used as an analogy for the Holy Trinity for fire generates light and heat. Nevertheless, the flame, its light and its heat are one entity. From the moment the flame begins, from that moment light and heat also begin.
Water: It was written, “The wellspring of wisdom is a flowing brook” (Prov 18:4) The well, spring and stream have been used also as an analogy for the Holy Trinity: Just as the spring and the stream produced from a well are not separate and yet there are in fact three visible objects and three names yet they all have the same water.
Love: Lover, Beloved and Love. "And he saw the Spirit of God descending like a dove and lighting on him. And a voice from heaven said, ‘This is my Son, whom I love and with him I am well pleased’" (Matt. 3:16-17). God the Father loves God the Son through the Holy Spirit.
So why should we not forgot about the Trinity since it is so complicated. Many people have done this over the years. Unitarians came into exist because they denied the Trinity.
Basically, though, the reason to keep proclaiming the Trinity as true is because of who Jesus is and has been revealed to us through Scripture. If there is no Trinity, Jesus is not God and the Holy Spirit is not God. Therefore, Jesus has no salvific power and his crucifixion and resurrection have no world-altering effect beyond the whims of some tyrant god. If there is no Trinity, the Holy Spirit has no power to be present with us, to comfort and advocate for us because the Holy Spirit is not God.
Finally, prayer: if God is not triune, than the Spirit is not present with us in prayer. If God is not triune than God does not desire friendship with us but servitude. Trinity frees us to follow the God that is love fully, only limited by our weakness. And even then, free to be transformed by the God that is love through power of God’s triunity.
From the UMC Articles of Religion
Article I - Of Faith in the Holy Trinity
There is but one living and true God, everlasting, without body or parts, of infinite power, wisdom, and good; the maker and preserver of all things, both visible and invisible. And in unity of this Godhead there are three persons, of one substance, power, and eternity—the Father, the Son, and the Holy Ghost.